This invention concerns the return of machine tool coolant to a filter apparatus. It is common practice in machine tool installations to collect the coolant draining from the cutting tools and the chips entrained therein in trenches or troughs extending below the machine tools, the drained coolant flowing down the trough to be collected in a sump from where it is pumped back to a filter apparatus.
As described in EP 1122024, industry trends have resulted in quite shallow depth above grade troughs being used to collect the coolant and chips.
The lift apparatus described and claimed in that patent was invented by the inventor named in this application to enable coolant in shallow streams to be lifted and collected in a tank so as to be able to be pumped to filter apparatus by a conventional pump.
Another problem has been encountered in such installations, in that relatively large steel or other ferrous metal objects occasionally fall into the trough, such as broken cutting tools, large bolts, or other machine parts, etc. These objects can cause damage to pumps, blockage in the piping, etc., particularly where aluminum chips are being generated and the equipment is designed to handle only aluminum turnings and chips.
The lift apparatus described in EP1122024 is very effective at removing large objects from the trough along with the chips and coolant, and depositing the same in a collecting tank.
It has heretofore been proposed by the present inventor to use a chip shredder conveyor between the lift station and a collector tank to reduce the size of the chips prior to pumping the coolant and chips from the collector tank back to the filtration apparatus. These conveyors have the ability to chop the chips that often form to be of a smaller size to prevent blockages and to achieve improved performance of the filter equipment. However, such conveyors do not operate reliably, particularly when large balls of chip turnings are present, which sometimes occurs.
U.S. Pat. No. 6,406,635 describes locating an inducer chopper in the inlet of a pump to chop the chips to a smaller size prior to pumping the same. This arrangement is limited in the size of objects which can be handled. The pump itself has a recessed impeller to avoid the wearing contact of chips with the impeller surfaces. This results in low pumping efficiency since it relies on induced vortices to create pumping action rather than direct pumping action by the impeller.
U.S. Pat. No. 3,973,866 describes a chopper pump in which cutting edges on the impeller blades are used to cut particles in the pumped liquid, and also includes a rotary tool ahead of the impeller to slice larger solid particles prior to entering the pump.
Large steel objects present a hazard to such conveyors and pumps and the associated piping.
It is the object of the present invention to provide a method and apparatus for efficiently and reliably recirculating coolant liquids in which chips and occasionally present items of ferrous metal debris to filtration apparatus from a shallow depth flow of machining coolant with equipment which can operate for long periods without replacement.
It is a further object to provide a method for reliably removing ferrous debris contained in shallow streams of machine tool coolant.